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Land or land and house is normally a personal property of the Thai spouse
When you followed the required land office procedure for land acquisition by a Thai married to a foreigner, then the property is technically owned by your Thai spouse and at the Thailand Land Department registered as her personal property. This procedure is required because you as a foreigner are not allowed to own land, not even as a joint marital asset of husband and wife. You can find info on the land office procedure here...
Refund of personal payments
Irrespective the fact that the property is registered as a personal asset of your wife when the house was bought, in a divorce you may be entitled to a refund of all money invested that came from your personal property or part of the money that came from marital assets or marital account. It is therefore important that you keep all evidence of any payments and money transfers made. It is during the course of the marriage not such a bad idea to make a form of yearly accounting of your personal assets and marital assets with your wife, because when the marriage would end, say death or divorce after 10 years, it would be very difficult to prove what is personal and marital, especially because the law states that in case of doubt (whether or not something is personal or marital) it is considered marital and subject to equitable distribution. Your wife could say, the property is mine and show the land office declaration you signed 10 years ago (and therefore claim that the home is not divided as a marital asset because it is her personal property). If you do not have any proof that you paid for it you do not have a strong case, at best you would then be entitled to an equal division pursuant to section 1474 Civil Code. Find more info on property of husband and wife and personal property here...
You may have the legal right to get 50% or more when it is wholly paid from your personal property, however it is depended on:
consent and performance of your wife
a court judgement in case of dispute
It may not be easy to get a positive court outcome in your favor, but you can improve your position by:
enter into a prenuptial agreement before marriage listing both your personal assets at the time of marriage (if she has no assets at the time of marriage she cannot claim the house is bought with her money after the marriage)
maintaining proof of payments from you personal assets (keep proof of money transfers and keep a form of yearly accounting of personal and marital property)
a legal declaration of your wife (signed witnessed) in which your wife confirms the true source of the money or that she owns the house as a community marital property belonging to you and her and acquired during marriage